Selective GaAs fine stripe structures, aligned along ⟨011⟩ direction, were grown by atmospheric‐pressure metalorganic chemical vapor deposition using diethylgalliumchloride. The width of the (100) top surface of the triangle‐shaped selective epilayers could be changed from 0 to 25 nm by controlling the growth temperature, and was independent of the growth time. This phenomena can be explained by reevaporation enhancement effect of reactant species containing chloride and two‐dimensional nucleation.